Angiotensin II is an active compound of the renin-angiotensin system, and has powerful vasopressor action and stimulating action for the synthesis and secretion of aldosterone in the adrenal cortex. It is also known to be a substance causing hypertension. Its action is considered to be caused through a specific receptor on various target organs such as adrenal cortex, kidneys, arterioles and the peripheries of sympathetic nerves. Because of such a technical background, a number of angiotensin II antagonists have been reported with a view to developing a therapeutic for hypertension.
Among them, a tetrazolylated biphenylmethane derivative on which the present inventors have previously filed an application (WO94/04516) and which is represented by the following formula (6): ##STR1## wherein R.sup.1 represents a lower alkyl group and ring A represents a cycloalkane, cycloalkene or benzene ring; or a salt thereof is known to have excellent angiotensin II antagonistic action and be useful as a therapeutic for circulatory diseases such as hypertension, heart diseases and cerebral apoplexy.
As a process for producing the above biphenylmethane derivative (6), described in the international publication WO94/04516 is a process to obtain the derivative, as described in the below-described reaction scheme, by reacting a 2-(protected amino)-1,3,4-thiadiazole (7) with a protected tetrazolylated biphenylmethylbromide (8), eliminating the protecting group from the tetrazolyl group, also eliminating the amino-protecting group and then reacting with an acid anhydride (5). ##STR2## wherein R.sup.3 represents an amino protecting group, R.sup.4 represents a tetrazolyl protecting group (for example, triphenylmethyl group) and R.sup.1 and ring A have the same meanings as defined above.
The above process is however accompanied with the drawback that the protection of a tetrazolyl group is essential so that an eliminating operation of the protecting group is required, which means increase of the steps and lowering of the yield.
Accordingly, an object of the present invention is to provide an industrially advantageous process of a tetrazolylated biphenylmethane derivatives (6) or salts thereof.